This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-197203, filed Jul. 12, 1999; and No. 2000-126072, filed Apr. 26, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a cathode ray tube apparatus. In particular, the present invention relates to a cathode ray tube apparatus incorporating an electron gun assembly capable of compensating for dynamic astigmatism.
In general, a color picture tube 11, as shown in FIG. 1, has an envelope consisting of a panel 10 and a funnel 14 coupled integrally with this panel. On an interior face of this panel 14, there is formed a phosphor screen consisting of a stripe or dot shaped three-color phosphor layer that emits blue, green, and red lights, that is, a target 12. A shadow mask 13 having a number of apertures at its inside is mounted in opposite to this phosphor screen 12. On the other hand, an electron gun assembly 17 for emitting three electron beams 16B, 16G, and 16R is arranged in a neck 15 of the funnel 14. Then, the three electron beams 16B, 16G, and 16R emitted from this electron gun assembly 17 are deflected by horizontal and vertical deflecting magnetic fields generated from a deflection yoke 19 mounted on the funnel 14, and are directed to the shadow mask 13. The phosphor screen 12 is scanned horizontally and vertically with the electron beams 16B, 16G, and 16R passing through the shadow mask 13 so that a color image is displayed.
In such a color picture tube, in particular, an electron gun assembly 17 has an inline type structure for emitting three electron beams 16B, 16G, and 16R in line, consisting of a center beam 16G and a pair of side beams 16B and 16R on both sides thereof. In addition, a side beam through hole of a grid located at a relatively low voltage side and a side beam through hole of a grid located at a high voltage side grid, both forming a main lens portion of the electron gun assembly are not aligned and are eccentrically arranged. As a result, there is widely used practically a self convergence system inline type color picture tube in which three electron beams are converged at a screen center, a pin cushion shaped horizontal deflection magnetic field and a barrel shaped vertical deflection magnetic field are generated by a deflection yoke 19, and the three electron beams 16B, 16G, and 16R emitted in line are self converged on a screen area.
In such a self-convergent inline type color cathode ray tube, the electron beams passing through the non-uniform magnetic field is subject to the astigmatism. For example, as shown in FIG. 2A, the electron beams 16B, 16G, and 16R are subjected to forces indicated by arrows 3H and 3V by the pin cushion shaped magnetic field 1. As a result, as shown in FIG. 2B, a beam spot 4 of an electron beam is distorted on the periphery of the phosphor screen. The deflection aberration to which these electron beams are subjected occurs because the electron beams enter an excessively focused state in the vertical direction, and a halo 5 (blurring) is generated in the vertical direction. The deflection aberration to which the electron beams are subject becomes greater as the tube becomes larger, and the deflection becomes wider. Then, the resolution of the phosphor screen periphery is significantly degraded.
Means for solving degradation of the resolution due to such deflection aberration is disclosed in Japanese Patent Application Laid-open Nos. 61-99249, 61-250934, and 2-72546. These electron gun assemblies each, as shown in FIG. 3, consist of a first grid G1 to a fifth grid G5. An electron beam generating section GE, a quadruple lens QL, and a final focusing lens EL are formed along the traveling direction of the electron beam. As shown in FIG. 4A and FIG. 4B, two trios of asymmetrical electron beam through holes 7B, 7G, 7R, 8B, 8G, 8R each are provided on an opposite face of the respective grids G3 and G4, and the quadruple lens QL of each electron gun assembly is formed.
The lens powers of these quadruple lens QL and final focusing lens EL are changed in synchronism with the magnetic field of the deflection yoke, whereby the deflection aberration applied to the electron beams deflected at the periphery of the screen due to the deflection magnetic field is corrected. In this manner, a beam spot having a good spot shape in the screen can be obtained.
However, even if such correcting means is provided, the deflection aberration due to the deflection yoke is strong. Even if a halo portion of the electron spot can be eliminated, but the horizontal elongated phenomenon in which the electron beam spot is deformed in a horizontal direction cannot be corrected. In order to correct this horizontal elongation phenomenon, it is required not only to correct the deflection aberration due to the quadruple lens QL, but also to correct the beam shape at an electron beam generating section in synchronism with the deflection magnetic field.
Such color picture tube apparatuses are disclosed in U.S. Pat. No. 4,319,163 and Japanese Patent Application Laid-open No. 8-87967. In these color picture tube apparatuses disclosed in these publications, a second grid is divided into two sections. A grid on the first grid side of the second grid has a circular electron beam through hole, and a grid on a third grid side of the second grid has an horizontally elongated electron beam through hole. In an electron gun assembly of this tube apparatus, a focusing power of a main lens portion is changed, and a dynamic voltage synchronized with a deflection current of a deflection device is applied to the grid on the third grid side. According to such color picture tube apparatus, at a triode portion for generating electron beams, electron beams are dynamically controlled in synchronism with the deflection current of the deflection device, and the focused states of the main lens and the quadruple lens arranged at the main lens are changed. Therefore, according to such structured electron gun assembly, a horizontal deformed phenomenon can be eliminated more significantly, and electron beams can be focused at the periphery of the screen more properly than a conventional dynamic focus electron gun assembly in which the focused states of the main lens and the quadruple lens disposed in the vicinity of the main lens are changed.
However, in the color picture tube device disclosed in the aforementioned publication, from the outside of the color picture tube apparatus, it is required to apply a focus voltage having an intermediate level; a dynamic focus voltage which increases in synchronism with the deflection current of the deflection device with the focus voltage having the intermediate level being a reference; a acceleration voltage having low level applied to the grip on the first grid side of the second grid; and a dynamic focus voltage that increases in synchronism with the deflection current of the deflection device applied to the third grid side of the second grid with this low level acceleration voltage being a reference.
In such electron gun assembly, in comparison with an electron gun assembly for a color picture tube device it is required to newly apply a dynamic focus that performs general dynamic focus, voltage that increases in synchronism with the deflection current of the deflection device with the acceleration voltage having the low level being a reference. In addition, it is required to newly provide a lead wire for supplying a voltage to a stem portion. For this reason, there is a possibility of lowering withstanding voltage characteristics due to an addition of this lead wire, and there is a problem in reliability. In addition, in the color picture tube apparatus provided with this lead wire, re-designing of the stem portion is required. Further, in a driving device for supplying a voltage also, it is required to newly add a circuit for generating this dynamic voltage, and there is a problem that such circuit addition causes higher cost.
As described above, in a color cathode tube of self-convergence inline type, non-uniform deflection magnetic field is generated from a deflection yoke. Thus, the astigmatism is applied to electron beams in the deflection magnetic field, and the beam spot at the periphery of the screen is distorted. For this reason, the resolution of the periphery of the screen is significantly degraded.
As means for solving degradation of the resolution due to such deflection aberration, a voltage that changes in synchronism with the deflection magnetic field is applied to a grid that forms a final focusing lens of the electron gun assembly, and a quadruple lens is formed in the vicinity of the final focusing lens. With such arrangement, there is provided an electron gun assembly having a dynamic focus system such that a deflection aberration resulting from a deflection magnetic field can be compensated. However, in this dynamic focus system electron gun assembly, a halo of the beam spot can be eliminated, but the horizontal deformation of the beam spot cannot be corrected. Therefore, there is a problem that the resolution of the periphery of the screen cannot be well improved.
As a color picture tube that improves the resolution of the periphery of the screen, focusing power of the main lens is changed in synchronism with the deflection magnetic field, and the shape of electron beams is corrected at the electron beam generating section. However, in such color picture tube, there must be additional provided a lead wire for supplying to a stem a dynamic voltage. There is a possibility that the withstanding voltage characteristics of the stem are degraded due to an addition of the lean wire, and there is a problem in reliability. In addition, it is required to newly design a stem. Further, with respect to the driving circuit for supplying a voltage, it is required to newly provide a circuit for supplying a dynamic voltage, and there is a problem that such circuit provision causes higher cost.
It is an object of the present invention to provide a cathode ray tube apparatus comprising an electron gun assembly that improves the shape of a beam spot and improves the resolution of image on the overall of the screen without requiring extensive provision of a stem lead wire.
According to the present invention, there is provided a cathode ray tube comprising: an electron beam generating section; an electron gun assembly having a main electron lens portion formed of a plurality of grids, each focusing on a target at least one electron beam emitted from the electron beam changes is applied.
Alternatively, one of the two grids connected to each other by the resistor is not fixedly supported by an insulation support for supporting and fixing the grids of the electron gun assembly. This electrode is fixedly supported by at least one grid to which a voltage that dynamically changes, the grid being adjacent to the electrode by means of an dielectric whose specific dielectric constant ∈s is 1 or more.
Of course, a dielectric Ci having the above arrangement is disposed so as not to have an effect on electron beam transmission. The dielectric Ci is made of a material that does not substantially have temperature dependency.
With such arrangement, a part of the dynamic voltage supplied to the fourth grid is supplied to the third grid through an electrostatic capacity between the second and third grids and through an electrostatic capacity between the third and fourth grids. Then, a potential difference is generated between the second and third grids, and an asymmetrical lens is operated. In addition, at the same time, voltages applied to the second, third, and fourth grids are changed in synchronism with the deflection magnetic field. Thus, between the second grid and the fourth grid, a cylindrical lens component becomes strong at the same time, the divergence action in the horizontal direction generating section; and a deflection yoke for generating a magnetic field for scanning a screen by the deflected electron beam, wherein an electron beam forming section for generating electron beams is composed of first grid to fourth grid, a first grid of the electron beam forming section is composed of a plate electrode, is grounded at the outside of the tube; or a negative potential is slightly supplied, a second grid is made of a planar electrode, and is connected to a third electrode by a resistor disposed in a the tube; an acceleration voltage of about 600 V to 800 V is supplied to the second grid, this voltage is supplied to the third grid by a resistor disposed in the tube, and a voltage that change in synchronism with a deflection current of the deflection device is applied with a middle level focus voltage of about 7 kV to 9 kV being a reference. Then, an asymmetrical lens is formed between the second lens and the third lens.
Alternatively, in the above arrangement, the second grid side of the third grid has a protruded portion at a peripheral of an electron beam through hole.
Further, there are disposed at least one electrode connected to the resistor; and a dielectric whose specific dielectric constant ∈s is 1 or more between at least one electrode connected by the resistor and at least one grid to which a voltage that dynamically between the second and third grids is offset, and operation is effected so as to help the focusing action in the vertical direction.
In the triode, by generating such action, a diameter of a crossover image, i.e., an objective point in the vertical direction is increased as the deflection magnetic field increases. In addition, a divergence angle in the horizontal direction is not increased extremely. Thus, there is achieved an advantageous effect that the diameter of the crossover image is reduced without causing an increase in aberration at the main lens portion due to the spread of the electron beams in the horizontal direction. This makes it possible to eliminate the horizontal elongation phenomenon at the periphery of the screen more efficiently, and cause electron beams to be focused more properly at the periphery of the screen.
At the inside of the electron gun assembly, a potential difference can be generated between the second and third grids. Thus, it becomes unnecessary to newly add a dynamic focus voltage that increases in synchronism with the deflection current of the deflection device with an acceleration voltage having a low level being a reference, and it becomes unnecessary to newly provide a lead wire for supplying a voltage to a stem portion. Therefore, there can be avoided a problem that the lowering of the withstanding voltage due to an increase in this lead wire causes reliability. In addition, in the color picture tube device, it becomes unnecessary to re-design a stem portion for this lead wire increase. At the same time, in the driving device for supplying a voltage also, in particular, it becomes unnecessary to newly add a circuit for forming this dynamic voltage. Therefore, there is no problem that such circuit addition causes higher cost, and a high dignity cathode ray tube can be easily provided.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.